Internet Engineering Task Force (IETF) D. Ceccarelli Request for Comments: 8258 Ericsson Category: Standards Track L. Berger ISSN: 2070-1721 LabN Consulting, L.L.C. October 2017
Generalized SCSI: A Generic Structure for Interface Switching Capability Descriptor (ISCD) Switching Capability Specific Information (SCSI)
This document defines a generic information structure for information carried in routing protocol Interface Switching Capability Descriptor (ISCD) Switching Capability Specific Information (SCSI) fields. This "Generalized SCSI" can be used with routing protocols that define GMPLS ISCDs and any specific technology. This document does not modify any existing technology-specific formats and is defined for use in conjunction with new GMPLS Switching Capability types. The context for this document is Generalized MPLS, and the reader is expected to be familiar with the GMPLS architecture and associated protocol standards.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
The context for this document is Generalized MPLS, and the reader is expected to be familiar with the GMPLS architecture, associated terminology, and protocol standards: notably, but not limited to, [RFC3945], [RFC4202], [RFC4203] and [RFC5307].
The Interface Switching Capability Descriptor (ISCD) [RFC4202] allows routing protocols such as OSPF and ISIS to carry technology-specific information in the Switching Capability-specific information field, see [RFC4203] and [RFC5307]. The format of an SCSI field is dictated by the specific technology being represented as indicated by the ISCD Switching Capability field. Existing Switching Capabilities are managed by IANA in the "Switching Types" registry <http://www.iana.org/assignments/gmpls-sig-parameters> and the related "IANA-GMPLS-TC-MIB" definitions.
Ceccarelli & Berger Standards Track [Page 2]
RFC 8258 Generalized SCSI October 2017
[RFC7138] introduced a "sub-TLV" structure to its technology-specific SCSI field. The sub-TLV-based approach allows for greater flexibility in the structure, ordering, and ability to support extensions of the SC-specific format. This Sub-TLV approach is also used in [RFC7688].
This document generalizes this approach and defines a new generalized SCSI field format for use by future specific technologies and Switching Capability types. The generalized SCSI carries SCSI-TLVs that may be defined within the scope of a specific technology or shared across multiple technologies (e.g., [AVAIL-EXT]). This document also establishes a registry for SCSI-TLV definitions that may be shared across multiple technologies.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
The reader is expected to be familiar with GMPLS terminology (e.g., as found in [RFC3945]) as well as the terminology used in [RFC4202], [RFC4203], and [RFC5307].
The Generalized SCSI is composed of zero or more variable-length TLV fields each of which is called an "SCSI-TLV". There are no specific size restrictions on these SCSI-TLVs. Size and other formatting restrictions may be imposed by the routing protocol ISCD field (refer to [RFC4203] and [RFC5307]). Please refer to [RFC3630] for the treatment of malformed Link TLVs.
Type (2 octets): This field indicates the type and structure of the information contained in the Value field.
Length (2 octets): This field MUST be set to the size, in octets (bytes), of the Value field. The value of the field MUST be zero or divisible by 4. Note that this implies that the Value field can be omitted or contain padding.
Value (variable): A variable-length field, formatted according to the definition indicated by value of the Type field. This field can be omitted for certain types.
The ISCD can include a Generalized SCSI when advertising technologies whose Switching Capability definition references this document. The corollary of this is that the Generalized SCSI MUST NOT be used for ISCDs of technologies whose Switching Capability definition do not reference this document.
The Generalized SCSI MAY contain a sequence of zero or more SCSI- TLVs. Sub-TLV parsing (format) errors MUST be treated as a malformed ISCD. SCSI-TLVs MUST be processed in the order received and, if re- originated, ordering MUST be preserved. Unknown SCSI-TLVs MUST be ignored and transparently processed, i.e., re-originated when appropriate. Processing related to multiple SCSI-TLVs of the same type may be further refined based on the definition on the type.
This document does not introduce any security issue beyond those discussed in [RFC4203] and [RFC5307]. As discussed there, the information carried in ISCDs is not used for Shortest Path First (SPF) computation or normal routing, and the extensions here defined do not have a direct effect on IP routing. Tampering with GMPLS Traffic Engineering (TE) Link State Advertisements (LSAs) may have an effect on the underlying transport network. Mechanisms such as those described in [RFC2154] and [RFC5304] to protect the transmission of this information are suggested.
This document defines a new SCSI-TLV that is carried in the SCSI field of the ISCDs defined in [RFC4203] and [RFC5307]. The SCSI-TLV includes a 16-bit type identifier (the Type field). The same Type field values are applicable to the new SCSI-TLV.
IANA has created and will maintain a new registry, the "Generalized SCSI (Switching Capability Specific Information) TLV Types" registry under the "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Parameters" registry.
The initial contents of this registry are as follows:
Value SCSI-TLV Switching Type Reference --------- ----------------------- -------------- --------- 0 Reserved [RFC8258] 1-65535 Unassigned (value list)
New allocation requests to this registry must indicate the value or values to be used in the Switching Type column.
The registry should be established with registration policies of "Specification Required", see [RFC8126].
[AVAIL-EXT] Long, H., Ye, M., Mirsky, G., D'Alessandro, A., and H. Shah, "OSPF-TE Link Availability Extension for Links with Variable Discrete Bandwidth", Work in Progress, draft-ietf-ccamp-ospf-availability-extension-10, August 2017.